2.75" wheels not touching the ground

I have a 6 wheel drive with two 2.75" omni wheels in the front two 2.75" traction wheels in the middle and two 2.75" omni wheels in the back. It seems as though the traction wheels are slightly smaller than the omni wheel. How can I fix this problem?

https://drive.google.com/open?id=0B4jZDlNwY0bcRXVxdFc4UUZ5YU0
https://drive.google.com/open?id=0B4jZDlNwY0bcMFVGaVpXWnJLcTQ

The the bearings that look like - not ___ ( a dash means a hole)

One fix would be putting rubber bands and/or zip ties around the traction wheels. That should at least work as a last resort.

DO NOT try this. The rubber band will cause more problems. Just use the special looking bearings to make it work

We had no problems with rubber bands under the tire. Care to elaborate on the problems?

They are 2.75" traction wheels so adding that bearing will make it higher than the rest of the wheels.

https://drive.google.com/open?id=0B4jZDlNwY0bceDh6aTNaSzVpTXM
Use the one one the top left

I know the 2.75" wheel that I’m using is like 4 pieces of paper off the ground tho…

They’re called pillow block bearings. Just take off the tires, add a rubber band, and put it back on.

Won’t it come off since the wheel is so thin.

You can use pillow bearing blocks on all of your wheels, and then lower the middle ones by adding washers between the pillow bearing and the metal it’s mounted to.

No, the rubber band is in place between the plastic wheel and the tire, so you shouldn’t actually see the rubber band after it’s on.

Would just wrapping couple of zip ties solve it? Or should I just adding a single rubber band under the tire?

I think zip ties would make the wheel not round because of the locking part of the zip tie, but yes, really any sort of padding between the tire and the plastic portion will work. I said rubber bands because it was the most obvious/readily available solution to me.

You can rotate the zip tie under the plastic of the tire.

Yes, you can. Again, really any padding to increase the radius of the wheel will work.

Just by skimming through the earlier posts in this thread, I noticed:

  1. Your traction wheels (presumably near the center of the chassis) are approximately 4 sheets of paper off the ground.

  2. You do not have any space to take the chassis apart and re-align it with pillow bearings.

  3. You are trying to fix the spacing discrepancy by using rubber bands and/or rubber matting wrapped around the radius of the wheel.

Taking into consideration that all of the above statements are correct, I have some advice:

  1. Test the spacing issue on a field tile if you have not done so. Field tiles especially worn ones compress slightly causing the robot to “sink down”. This may solve the issue especially if you were testing it on a hard surface such as wood, tile or concrete.

  2. PLEASE do NOT put anything around your drivetrain base, it may work while you are testing, but in competition it will likely come off of you wheels which is bad for your robot, and litters the field for other robots.

  3. If you have any spare time, I recommend taking your chassis apart and aligning the wheels using pillow bearings and spacers in the worst case.

I would greatly appreciate it if you could share your results!

We had this issue, and nobody noticed it during Inventor prototyping. Come build time, and there was much swearing once this was discovered. We just removed the middle wheel altogether, with 4 omnis in the corners. We’ve never had an issue of being pushed, but we did have the robot almost roll it self sideways off the table.